Opto-electric hybrid modules are typically produced by: individually producing a flexible circuit board including an electric circuit provided on a surface of an insulation layer, and an optical waveguide including an under-cladding layer, a core and an over-cladding layer stacked in this order; bonding a back surface of the insulation layer of the flexible circuit board to a surface of the over-cladding layer of the optical waveguide with an adhesive agent; and mounting an optical element on a predetermined portion (mounting pads) of the electric circuit. The electric circuit has a rectangular sectional shape. The opto-electric hybrid modules are flexible, and are advantageous for use in a bent state in a small space and for use in a movable portion such as a hinge portion to meet a recent demand for size reduction of electronic devices and the like.
An opto-electric hybrid module as shown in a transverse sectional view of FIG. 4 (see, for example, PTL1) is proposed, in which an electric circuit including mounting pads 4a and an electric circuit body 4 are provided directly on a surface of an over-cladding layer 13 of an optical waveguide W1 (without provision of an insulation layer) for simplification of the production method thereof. In the opto-electric hybrid module, the electric circuit body 4 is generally coated with a cover lay 14 of an insulative resin. In FIG. 4, reference character 5 designates an optical element, and reference character 5a designates electrodes of the optical element 5. Reference character 11 designates an under-cladding layer of the optical waveguide W1, and reference character 12 designates a core of the optical waveguide W1.
An opto-electric hybrid module as shown in a transverse sectional view of FIG. 5 (see, for example, PTL2) is also proposed, in which a distance between an optical element 5 and a core 22 is reduced by forming an electric circuit including an electric circuit body 4 and mounting pads 4a on a surface of an under-cladding layer 21 of an optical waveguide W2 to thereby improve the optical coupling efficiency between the optical element 5 and the core 22. In the opto-electric hybrid module, the electric circuit body 4 is not covered with the cover lay 14 (see FIG. 4) but is covered with a part 23a of an over-cladding layer 23. In FIG. 5, reference character 22a designates positioning guides defined by parts of the core 22 to surround the mounting pads 4a for positioning electrodes 5a of the optical element 5 with respect to the mounting pads 4a. 
As described above, the opto-electric hybrid modules are required to be flexible and, therefore, the cover lay 14 and the part 23a of the over-cladding layer 23 each covering the electric circuit body 4 preferably each have a smaller thickness.